There are two types of PDF form, and knowing which one you have determines the fastest way to fill it in. The first is an interactive form, it has actual form fields built into the PDF, visible as text boxes and checkboxes you can click on and type into directly. The second is a flat form, it looks like a form but is really just a PDF image of one, with no clickable fields. Flat forms require a different approach.
Interactive PDF forms: open in your browser and type directly
If your PDF has real form fields, you can fill it in directly in any modern browser. Open the PDF in Chrome, Firefox, Edge, or Safari, just drag it onto a browser window. Click on the form fields and type your answers. Checkboxes can be checked by clicking them. Dropdown fields will show options when clicked.
Once you have filled in the form, save or download it. In Chrome and Edge, use the download button in the PDF toolbar. In Firefox, use the save function. The filled-in values are saved in the PDF and will be visible to the recipient without them needing to do anything special to see your answers.
For iPhone users: open the PDF in Safari and tap the form fields. iOS handles interactive PDF forms in the Safari PDF viewer reasonably well, though very complex forms with JavaScript dependencies may work better in the Adobe Acrobat app. For Android: Chrome handles most interactive forms in the same way.
Flat PDF forms: add text annotations
A flat form looks like a form but has no actual form fields. Clicking on it in a browser just selects the whole page. For these, you need to add text annotations on top of the form image.
PDFWhisk's signing and annotation tool lets you add text to any position on a PDF page by clicking to place a text element and typing your entry. You can position text precisely to fill in the visible blanks on the form. For checkboxes on a flat form, add a small X or tick character positioned over the relevant box.
Adobe Acrobat Reader (free) also supports adding text annotations and fill-and-sign elements to flat forms. Open the PDF, click the Fill & Sign tool in the toolbar, and use the text and check mark tools to place entries over the form.
Signing the completed form
If the form requires a signature after filling in, add the signature using the sign tool before downloading the final version. For forms that need both text entries and a signature, do both in the same session so the output is one coherent, completed PDF.
On iPhone, the sign tool in Safari's PDF viewer lets you draw a signature with your finger and place it on the page. This is usually the fastest route for signing and returning a form on a phone without needing a separate app.
Forms that need to stay editable
Occasionally a form needs to be filled in partially and then edited further later, or passed to someone else to complete a different section. For interactive PDF forms, this is straightforward, fill in your section, save, and send. The recipient can add to the fields you left blank.
For flat forms that have been annotated with text overlays, the annotations are usually saved as a permanent layer on the page and can be edited or deleted in PDF annotation tools. In Adobe Acrobat Reader, annotations added with the Fill & Sign tool can be clicked to edit before saving. In PDFWhisk, text elements placed on the form can be repositioned before downloading.
Government and official forms
Many UK government forms are PDFs that can be filled in interactively. HMRC's self-assessment forms, NHS registration forms, council application forms, and DWP evidence forms are typically designed as interactive PDFs intended to be completed on a computer. If the form feels unresponsive or the fields do not activate when you click them, it may be that the form uses Adobe-specific JavaScript features that only work fully in Adobe Acrobat Reader rather than a browser's built-in PDF viewer.
If a government form is not working in your browser's PDF viewer, download it and open it in Adobe Acrobat Reader (free download) rather than trying to fill it in the browser. Most Adobe-specific forms work correctly once opened in Acrobat.
Saving your completed form
Before downloading, check all fields are filled correctly. Scroll through every page, zoom in on small text fields, and verify checkboxes are marked correctly. For multi-page forms, check both the first and last pages carefully, these are the areas most commonly missed during review.
Save the filled-in form with a clear filename before sending or uploading. A name like John-Smith-Application-Form-May-2026.pdf is more useful to a recipient than form-filled.pdf or the generic filename the form came with.